I used to use a CPAP. The basic unit ran off 12V provided by the line lump power supply. I disconnected the humidifier when traveling and just got a 12V power cord with the appropriate connector that plugged into the cigar lighter socket by the TV. Ran fine all night. You do want to verify your particular unit does indeed run from 12V. All the ones I have seen do, but never hurts to be sure.

A direct conversion from 12v to 24vdc is more efficient than going from 12v through an inverter to make 110vAc ...then back through the Airsence10 power supply to 24vdc.
Each device that makes a conversion along the chain is never 100% efficient and therefore unnecessarily wastes power. Simply...If a device gets even slightly warm while doing its job of converting...that's wasted power that could otherwise be used to run the Cpap machine.